1. Field of the Invention
The present invention relates in general to desiccant assisted air conditioners, and relates in particular to a desiccant assisted air conditioning system having a heat pump device to provide a heat accumulation function and serving as a heat source for regeneration of desiccant material and as a cooling source for cooling process air.
2. Description of the Related Art
Desiccant assisted air conditioning apparatus is well known, for example in a U.S. Pat. No. 2,700,537. The system discloses a desiccant assisted air conditioning apparatus requiring a heat source in a temperature range of 100.about.150.degree. C. for regenerating the desiccant (moisture adsorbent), and heat sources such as electric heaters and boilers are primarily utilized. In recent years, desiccants which can be regenerated at lower temperatures in a range of 60.about.80.degree. C. have been developed, enabling the use of heat sources operating at lower temperatures.
FIG. 21 is a schematic representation of a typical example of such improved desiccant assisted apparatus combining a known motor-driven vapor compression heat pump (including refrigerating machine), and FIG. 22 is a psychrometric chart showing the operation of this example apparatus. In FIG. 21, the reference numeral 101 refers to a conditioning space; 102 refers to a blower; 103 refers to a desiccant wheel including desiccant material alternatingly communicatable with the process air and regeneration air; 104 refers to a sensible heat exchanger; 105 refers to a humidifier; 106 refers to a water supply pipe for the humidifier; 107.about.112 refer to air passages for process air; 140 refers to a blower for the regeneration air; 220 refers to a condenser as well as a heat exchanger between refrigerant and regeneration air (heating device); 121 refers to a sensible heat exchanger; 124.about.129 refer to air passages for regeneration air; 201.about.204 refer to cooling refrigerant passages. Numeral 240 refers to an evaporator for working as a heat exchanger between refrigerant and process air (cooling device). In FIG. 21, circled letters K.about.V represent the thermodynamic state of the air medium being processed to correspond to respective sites shown in FIG. 22, SA designates supply air, RA designates return air, OA designates outside air and EX designates exhaust air.
The operation of such an apparatus will be explained in the following. In FIG. 21, the ambient air from the room 101 to be conditioned (process air) is drawn through a passage 107 into a blower 102 to be pressurized and is forwarded to a desiccant wheel 103 through a passage 108. In the desiccant wheel 103, the humidity ratio of the ambient air is lowered by the removal of moisture from the ambient air to the moisture adsorbent in the desiccant wheel 103. During the process of adsorption, the heat of adsorption is released into the process air which rises in temperature. The process air with a warmer temperature and a lower humidity is forwarded through the passage 109 to the sensible heat exchanger 104, and is cooled by heat exchange with outside air (regeneration air). Then the cooled air is forwarded to an evaporator 240 through a passage 110 to be further cooled by the heat pump device and is forwarded to a humidifier 105 through a passage 112 to be cooled by water spraying or evaporative humidification in an isenthalpic process and is returned to the conditioning room 101 through a passage 113.
The desiccant material absorbs moisture during this process and needs to be regenerated. In this example, this is performed as follows. Outside air (regeneration air) OA is drawn into the blower 140 through a passage 124 to be pressurized and forwarded to the sensible heat exchanger 104. This outside air cools the process air and, in the process, raises its own temperature. The warm air OA flows into a next sensible heat exchanger 121 through a passage 125 and raises its temperature by heat exchange with the spent high temperature regeneration air after regeneration. The regeneration air from the heat exchanger 121 flows into a condenser 220 through a passage 126 so that it is heated by heat of condensation of the heat pump device to raise its temperature to a range of 60.about.80.degree. C., and its relative humidity is lowered. The regeneration air with a lowered humidity passes through the desiccant wheel 103 to remove the moisture from the desiccant wheel. Spent air from the desiccant wheel 103 flows through a passage 128 to enter the sensible heat exchanger 121 to preheat the regeneration air prior to regeneration, and flows through a passage 129 to be exhausted externally.
The above process can be explained with reference to the psychrometric chart shown in FIG. 22. The ambient air in room 101 to be air conditioned (process air: state K) is drawn into the blower 102 through the passage 107 to be pressurized, and flows through the passage 108 to reach the desiccant wheel 103 so that its humidity ratio will be lowered by adsorption of moisture to the moisture adsorbent in the desiccant wheel while its temperature rises (state L) by the heat of adsorption. The air with a lower humidity and a higher temperature flows through the passage 109 to reach the sensible heat exchanger 104, and is cooled by heat exchange with the regeneration air (state M). The cooled air flows through a passage 110 to reach the evaporator 240 to be further cooled by the heat pump device (state N) and is forwarded to a humidifier 105 through a passage 111 so that its temperature is lowered in an isenthalpic manner by water spraying or evaporative humidification (state P), and is returned through the passage 112 to the conditioning space 101. In the above manner, an enthalpy difference is produced between return air (state K) in the room and supply air (state P) for use for cooling of the conditioning space 101.
The desiccant is regenerated as follows. Outside air (OA: state Q) is drawn through the passage 124 into the blower 140, is pressurized, forwarded to the sensible heat exchanger 104, cools the process air and raises its own temperature (state R), flows into the passage 125 and the next heat sensible exchanger 121, exchanges heat with the spent high temperature air so that its own temperature rises (state S). Regeneration air from the sensible heat exchanger 121 flows through the passage 126 to reach the condenser 220 and is heated by the heat of condensation of the heat pump device to a temperature between 60.about.80.degree. C., so that its relative humidity is lowered (state T). The regeneration air having a lowered humidity flows through the desiccant wheel 103 thereby removing adsorbed moisture (state U). Spent outgoing air from the desiccant wheel 103 flows through the passage 129 to reach the sensible heat exchanger 121 to preheat the regeneration air prior to regeneration process, and lowers its own temperature (state V) and flows into the passage 129 to be exhausted out as waste air. The processes of regeneration of desiccant and dehumidification and cooling of the ambient air described above is repeatedly performed to provide the desiccant assisted air conditioning process. Thus, the regeneration air is defined as air to be humidified, and the process air is defined as air to be dehumidified in this specification.
In the desiccant assisted air conditioning system having such a configuration, the vapor compression refrigeration process combined with the desiccant regeneration cycle requires a condensation temperature of about 80.degree. C. In recent years, it has become desirable to replace CFC (chlorofluorocarbon) refrigerant with more environmentally acceptable ammonia as refrigerant in the vapor compression refrigeration cycling units; however if, it is desired to attain the condensation temperature in this range, the pressure requirement increases to an abnormally high range of about 42 Kg/cm.sup.2, resulting in an expensive air conditioning system to provide the necessary pressure endurance.
Therefore, there has been a need to develop a desiccant assisted air conditioning system to enable operation of the working fluid at low refrigerant pressures while offering high reliability, environmental compatibility and low cost.